POU domain proteins are DNA binding proteins that control the transcription of other genes. Their control has been found to be important in the development of numerous systems including the anterior pituitary and the epidermis in mammals and in neuron cell identity in C. elegans. We have identified a fragment of a pou gene by PCR using reverse transcription of RNA from embryonic chicken heart and degenerate primers based on a Drosophila pou amino acid sequence. The sequence analysis of the chicken pou fragment shows it to be clearly related to other pou genes previously identified, but to be divergent enough to suggest a new class of pou gene. This class has only one other member, called pou(c), in the zebrafish. The original goal of this project was to obtain the entire sequence of this chicken pou gene, to confirm that it is expressed in embryonic heart and to explore its role in development. However, by Northern analysis, RNAse protection assay and library screening, the mRNA of this gene is very rare in the chicken. Its homolog in mouse was easily found on Northern analysis and cloned from an 11.5 day mouse embryo cDNA library. Therefore, the project was continued in the mouse. The gene is expressed after day 11 in the embryo and ubiquitously in the adult mouse with the most abundant expression in the brain. The mRNA is 5.0 kb on a Northern blot. Four kilobases of the cDNA have been subcloned and sequenced. The remaining 1 kb will be found by screening an adult mouse brain library. We are presently defining the pattern of expression of this gene by in situ hybridization in whole mouse embryo and adult mouse brain. The POU family of genes has been shown to be important in transcription regulation both in the embryo and in the adult. We would like to explore the function of this new member of this family in the mouse.